Re: Leave outside of DO group???

[DrFranken <midrange@xxxxxxxxxxxx>]

I like James' explanation here but I stay more on the Practical side. If 
I copy a chunk of code or move a chunk of code and there are "GoTo" 
instructions I must carefully analyze the tags and determine if they 
also must be moved or if new ones must be created. Failure to do so can 
break program logic very badly. With a loop that utilizes Leave in 
addition to a normal exit 'at the bottom' it's very easily portable with 
essentially no risk to primary program flow.

Translation: I am lazy. :-)

        - Larry "DrFranken" Bolhuis

www.frankeni.com
www.iDevCloud.com
www.iInTheCloud.com

On 7/23/2013 7:37 PM, James H. H. Lampert wrote:

> Many years ago, there was a level of fanaticism involving structured
> programming, combined with a very primitive understanding of it. It was
> exemplified in the inordinate popularity of Pascal, which had no concept
> of "LEAVE," and only grudgingly included a GOTO.
>
> This primitive understanding assumed, in particular, that under normal
> conditions, an indexed loop always runs to completion, and should only
> exit early in case of an irrecoverable error. In fact, there's an
> obvious exception to this: table look-up. This led to numerous cases in
> which programmers were forced to choose between (1) storing the "found"
> value and continuing to waste processor resources iterating uselessly
> (perhaps at least skipping the "meat" of the loop), (2) substituting a
> DOWHILE or DOUNTIL construct, and handling the counter manually, or (3)
> using a GOTO.
>
> It's rather telling that when Niklaus Wirth, the ultimate structured
> programming maven, designed a language for actual production use (Pascal
> was never intended as more than a teaching language), it *did* have a
> "LEAVE" (I don't remember, offhand, what it was called).
>
> At any rate, where GOTO allows transfer of control to any labeled
> statement (in some languages, like traditional BASIC, all statements
> have labels), possibly even including transferring *into* a loop or
> inner-block in a way that bypasses any initialization, LEAVE simply
> exits the current iterative structure, going "out" the same way it would
> normally exit on completion, while ITERATE simply aborts the current
> iteration without actually exiting the loop.
>
> --
> JHHL